Thermostat



J. A. SPENCER THERMOSTAT Mar. 13, 1923. 1,448,240

Filed Apr. 8, 1921 I 1%/ ,ya

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Patente-JM. 13; 1923.

UNITED STATESl J 0H N A. SPENCER, OF REVERE, MASSACHUSETTS, ASSIGNOR TO SPENCER THERMOSTAT PATENT OFFICE.

COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

THERMOSTAT.

Application led April 8,

To all ywhom 'it muy concern:

Be it known that l', JOHN A. SPENCER, a citizen of the United States, residing at Revere, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in Thermostats; and I do hereby declare the following to be a full. clear, andeXact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to temperature controlled'apparatus and more particularly to devices of this character adapted to operate valves, switches and other mem-v bers when certain temperature limits are reached. l

Thermostatic controls for heating and other apparatus consisting of two dissimilar metals having different coefficients of thermal expansion have long been used. These controls have certain very decided objections, however, primarily due to the fact that the change of state takes place slowly in accordance with the change in temperature.

The object of the present invention is to provide an improved type of thermostatic control applicable to a variety of purposes and which overcomes the objections inherent in existing controls of this character.

With this object in View one feature of the invention contemplates the provision of a thermostatic device to which is imparted a sudden and rapid movement when a substantially predetermined temperature is reached. n l

' In the simplest and most efiicient form of the invention which has yet been devised a relatively thin sheet consisting of two metals having different thermal coefficients of expansion is formed into a non-develop- VVhen this device is heated to a certain point the sheet is suddenly caused to curve in a direction opposite to that in which it is initially curved, remaining in this condition until the temperature is substantially lowered. Upon reaching a predetermined lower limit of temperature, the sheet is suddenly arched or curved in the opposite direction. The configuration of thev thermostatic sheet is such that change of shape due to initial changes of temperature is normally resisted until the stresses 1921. Serial No. 459,773.

imposed by variation of temperature overcome this normal resistance, the thermostatic sheet thereafter abruptly changing to a shape of opposite curvature. The action of this device may be compared to the principle of a-.toggle lever having a spring which normally holds it in an inclined or broken position. In the present case the unequal expansion or contraction of the metals forming the disk provides the force for reversing the curvature of the nondevelopable sheet.

In the accompanying drawings illustrating the preferred form of the invention F ig. l represents the invention embodied in an electric flatiron and used for controlling the flow of current to the iron; Fig. 2 represents the new thermostatic device devoloped upon the surface of a sphere and Fig. 3 illustrates a somewhat different form of control.

The illustrated embodiment of the invention is shown particularly in connection with the thermostatic contro-l of electric circuits in which connection the present invention has particular utility, owing-to the quick breaking of the circuit which results from the sudden reversal of shape of the thermostatic sheet. Referring to the accompanying drawings the thermostatic control is indicated in Fig. 2 as a composite sheet made up of two materials, in this instance two metals such as iron and brass, having vdifferent thermal coefficients of expansion so that a change in temperature will cause unequal expansion and contraction of opposite faces of thesheet. This sheet is shaped into a cupped portion or non-developable surface, as, for example. by forming a spherical projection 10 in a flat sheet l1. If a thermostatic sheet is thus shaped and constructed it will be found that upon raising the temperature the unequal expansion of the materials forming the sheet will cause a tendency to flatten the cupped surface until at a predetermined temperature a sudden curving of the nondevelopable surface into the opposite direction occurs. which reversal of shape or flexure will he maintained until the temperature has been substantially lowered. Thereafter upon reaching asubstantially predetermined temperature the sheet will suddenly return to 'its initiakshape. In both of these movements the reversal of curvature is exceedingly abrupt and is caused by the expansion and contraction of the rhaterials ot' which the thermostatic sheet is composed. Free expansion and contraction ot the inner portion of the dent or curve ot the sheet is opposed or prevented b the material surrounding said portion. pon rise of temperaturethe expansion of the materials of the inner portion causes stresses to be set up in the materials. llVhen these stresses are sucient to cause the device to reach a condition ot instability (this condition is reachedA at a predetermined temperature) the ensuing sudden liberation oi' the stored stressesed'ects a sudden movement ot said portion, the movement occurring automatically.

'llhe uses to which a thermostatic control may be put are manifold especially in connection with the control ot electric circuits as the action ot' the non-developable sheet is sudden and positive and the reversal oi shape occurs with considerable force, ydepending upon the thickness of the sheet and the area ot the surface which undergoes the change. For example, ,the illustrated embodiment is shown as applied to an electric tlatiron comprising a presser member 15, a shell 16 and a handle 18. 'llhe flatiron is heated by the usual coil 20 connected into an electric circuit through leads 21 and 22. The thermostatic control is inserted in one side of the circuit, as shown, and may consist of a curved sheet 23 of two dissimilar metals' retained at its opposite edgesl in brackets 24 and 25 secured to a base 26 ot insulating material. The arched control memberV 23 is provided with a contact 28 which cooperates with a stationary contact 30 secured tothe base member and connected with a lead 32. The base member and elements carried thereby may be conveniently'insulated from the iron inA anyl suitable manner as by. insulator bushings or sleeves 36. 1W ith such a construction the How of current to the heater resistance isvautomatically cut off when an excessive telnperature limit is reached, the arched sheet 23. at this vpoint suddenly breaking the cirvcuit through the two contacts 28 and 30.

When the temperature of thethermostatc sheet has been reduced (that is, changed in opposite sense or direction) to a predetermined pointit will return to its initial position and close the circuitv It will be obvious that withv such a construction a positive and eective mechanism is provided for preventing overheating of the electric iron with thel consequent disastrous results. Furthermore the control willv operate indefinitely nwithout deterioration as the sudden breaking of theV circuit prevents any substantial arcing between the contact points. Fig. 3 illustrates a somewhat different form of thermostatic control, enabling a some what greater separation ot the contacts to be obtained. in this construction an arm 40 is'tormed of two dissimilar metals and is provided with a broken curve at l2 to form anon-developable surface. This arm is supported at el and the opposite tree end carries a Contact member t5 which may be adapted to cooperate with a stationary contact t6. lt the temperature of this arm be then raised it will be obvious that a curv ing ot the surface in the opposite direction at l2 will result in a substantial movement ot the contact 45 away from the stationary Contact Vl-6 with a correspondingly rapid breaking of the circuit,

lt should be understood that the present invention is not limited to any particular combination ot materials having different thermal coefficients of expansion but is intended to embrace in its scope any cornbination of materials having dissimilar thermal coeflicients of expansion sufficient to cause the characteristic reversal ot curvature. Furthermore, the two materials comprising the composite thermostatic sheet may be secured together in any desired manner by riveting, soldering, brazing or other- Wise although it is preferred to Vunite the materials comprising the sheet by welding o-r similar means to secure a substantially indivisible sheet. y'

From the foregoing it will be evident that in one'aspect the invention involves av thervmostatic device characterized by portions (the central and marginal portions of the upon each other with change of temperature to set up stresses the magnitude .of which changes upon cha-nge of temperature, at least one of the portions being formed of dierent metals or other components hav ing diii'erentl coefficients of expansion. the device reaching a condition of instability at a predetermined temperature by virtue of the arrangement of said portions and as a result of the differential expansion of the components due to' change of temperature,

whereupon said stresses becomes effective to change abruptly the relative position of said portions.

Having described the invention, what is claimed is:

1. A thermostat comprising a bimetallic sheet of thermostatic metal, the outer portion 'of the sheet forcing the inner portion to remain normally concave ordished on the side having. the higher thermal coefficient of Vexpansion and preventing free expansionv of said inner portion'when heated, said inner portion when heated tending to pass abruptly and automatically' to a position of an opposite curvature, and passing abruptly and automatically to said position at a predetermined temperature.

liti

2. A thermostat comprising a bimetallic sheet of thermostatic metal, the outer portion of the sheet forcing the inner portion to remain normally concave or dished on the side having the higher thermal coefficient of expansion and preventing free eX- pansion of said inner portion when heated,

said inner portion When heated passingv abruptly and automatically to a position of an opposite curvature, and resuming its original position abruptly and automatically when cooled to a predeterminedtemperature.

3. A thermostat comprising composite '.thermostatic material and means for conabruptly changing its shape.

4. A thermostat comprising composite thermostatic material an'd means for conning at least a portion of said material against free change of shape, thereby setting up internal stresses the magnitude of which change upon changes of temperature, the thermostat reaching a condition of instability at a predetermined temperature during heating and at a predetermined temperature during cooling, the material then abruptly changing it-s shape due to release of internal stresses stored up in the material by reason of the change of temperature to said predetermined value.

5. A thermostat comprising composite thermostatic material and means for confining at least a portion of said material against free expansion, thereby setting up internal stresses the magnitude of which change. upon changes of temperature, the

thermostat reaching a condition of instability when it-is heated to av predetermined temperature, the material then abruptly changing its shape due to release of internal stresses theretofore stored up in the material.

6. A thermostat comprising composite thermostatic material and means for confining at least a portion of said material against free expansion, thereby setting up internal stresses the magnitude of which change upon changes of temperature, the thermostat reaching acondition of`instability when it is cooled to a predetermined temperature, the material then abruptly changing its shape due to release of internal stresses theretofore stored up in the material.

7. A thermostat comprising thermostatic composite material, a portion of which is confined against free change of sha-pe, thereby setting up internal stresses the magnltude of which change upon changes of temperature, the material being so shaped that change of its shape is a discontinuous" function of the temperature. p

8. A thermostat comprising a sheet of composite thermostatic material, at least a portion of which is confined against free change of shape, lthereby setting up internal stresses the magnitude of Which change upon changes of temperature, the thermostat being so shaped that change of its shape is a discontinuous function of the temperature.

9. A thermostat comprising a composite thermostatic sheet having a non-developable depression adapted to change its shape suddenly on reaching a predetermined temperature.

10. A thermostat comprising a composite thermostatic sheet having a dent automatically adapted to store energy in the form of internal stresses ony change of temperature, said stresses at a predetermined temperature balancing and overcoming the resistance of. the dent to reversal, the dent then abruptly and automatically reversing.

1l. A thermostat comprising a compositey thermostatic sheet having a dent automatically adapted to store energy in the form of internal stresses on change of temperature, said stresses at a predetermined temperature balancing and overcoming the rcsista-nce of the dent to reversal, the dent then abruptly and automatically reversing, and upon change of temperature in the opposite direction to a predetermined value abruptly and automatically reverting toits original contour.

12. A thermostat comprising a composite thermostatic sheet having at leastA a part of its surface in the form of a dent of such a depth and shape that upon reaching a predetermined temperature the dent reaches a condition of instability and thereupon suddenly alters its'shape due to releaseof internal stresses caused by change of temperature.

13. A thermostat having a composite thermostatic sheet portion curved and a second portion which is stressed by the expansion of the first portion when heated andy which opposes the expansion of the first portion, the first portion when heated to a predetermined temperature tending to pass abruptly and automatically to another shape.

14. A thermostat having a composite thermostatic'sheet portion curved and a secr l5. A thermostat having a composite thermostatio sheet portion and a second portion which is stressed hy the expansion or contraction oit the irst portion with change of temperature and which opposes said eirpansion or contraction, the first portion when it attains a predeterminedtemperature tending` to pass abruptly and automaticallyto another shape.

16. thermostat comprising a plurality et united components having different coenficients of expansion9 said components heing normally flexed in one direction and tending to tiatten in response to temperature change in one sense thereby setting up stresses Whichoppose saidl tendency` until a predetermined temperature is reached, the stresses then changinpy the Hennie.

17. A thermostat comprising a'cornposite sheet having a cupped portion with different coetlioients oit expansion on opposite sides7 the peripheral portion oie the sheet being indienen adapted to he stressed by differential expansion oiA2 the opposite sides of the sheet until a predetermined temperature is reached, whereupon the stresses become effective ahrupt-ly to reverse the curva-ture of the cupped portion.

18. A the 1rnestatie device comprising portions arranged to react upon eachother with change ot temperature to set up stresses the magnitude oit which changes upon change oit temperature, at least one ot the portions being termed ot components having different coeiiicients of eiqiansionq the device reaching a condition oit instability at a predetermined temperature by Virtue ot the arrangement ot said portions and as a result or the change ot temperature, whereupon said stresses hecorne edective to change abruptly the rela-tive position ofhsaid portions.

JUHN A. SPENCER. 

